1. Field of the Invention
This invention relates to a circular polarized antenna, a design simulator for the antenna and a wireless module with the antenna.
2. Description of the Related Art
Circular polarized antennas are used in the field of BS (broadcasting satellite) and GPS (global positioning system) to allow good reception regardless of inclination of polarization plane. As a representative circular polarized antenna, a one-point feeding microstrip antenna is well known (e.g., Haneishi Misao et al., “Small and Planar Antennas”, The Institute of Electronics, Information and Communication Engineers, pp. 142-164, 1996, Corona Corporation). A circular polarized antenna can be designed by providing the microstrip antenna with a degenerate separation element to generate two modes orthogonal spatially. However, the antenna has a limitation in size that its radiating element has one side with a length of about half its working wavelength and, therefore, it is hard to downsize.
Since it is desired that wireless modules have a small and low-profiled antenna, various methods for downsizing, low-profiling and designing thereof are researched.
Some methods for downsizing, low-profiling and designing the one-point feeding circular polarized antenna are disclosed in, e.g., JP patent No. 2826224, JP-A-H08-51312, and JP-A-2001-251132.
JP patent No. 2826224 discloses a method that a notch is formed at both ends of a conductor in the direction of lines orthogonal at ±45 degrees to two resonance mode directions orthogonal to each other and with different phases by a degenerate separation element, either of the lines orthogonal at to at ±45 degrees to the resonance mode directions is made to agree to a deviation direction of the feeding point, whereby its resonance frequency is reduced to allow the downsizing of the antenna at a certain frequency.
JP-A-H08-51312 discloses a method that the antenna is downsized by using a liner antenna element having a loop base element.
JP-A-2001-251132 discloses a method that its radiating element is formed a single-wire rectangular spiral and its outermost perimeter length is more than its working wavelength and twice or less of the working wavelength so as to downsize the antenna.
However, in the method of JP patent No. 2826224, although the downsizing can be attained while keeping the two orthogonal modes needed to generate a circular polarized wave, it is hard to have good matching to the high-frequency circuit. Although a method of adjusting the reactance of input impedance is disclosed therein, the adjustment of resistance needs many trials and errors and, therefore, the design time must be prolonged.
In the method of JP-A-H08-51312, although good circular polarized wave can be generated by adjusting the aspect ratio of the rectangular loop element and the distance between the element and the grounding conductor, it is hard to have good matching to the high-frequency circuit. Although a method of adjusting the input impedance by loading a reactance in the radiating element and a method of adjusting the input impedance by parallel connecting the plural radiating elements are disclosed therein, its systematic design is hard to conduct and, therefore, the design time must be prolonged.
In the method of JP-A-2001-251132, although the downsizing is easy attained by making the radiating element spiral, it is needed that the structure is frequently adjusted in consideration of two conditions of the generation of circular polarized wave and the matching to the high-frequency circuit. Therefore, the design time must be prolonged.